Line check valves are well known in the art. Typically, such valves comprise a valve body having inlet and outlet passages communicating with a cavity in which the operating elements of the valve are located. In one arrangement, the inlet passage terminates at a valve seat in the cavity. A valve disk is provided at the valve seat, the disk being biased toward the valve set by coil springs so that it may slide on it, rest on it, or be moved away from it.
The prior art valves have a relatively small area for receiving the "cracking" pressure, i.e. the pressure necessary to initially move the disk away from the valve seat. Thus, in cases where the inlet pressure or inlet flow volume is low, the valve may not always operate. Furthermore, precise adjustment of the spring is difficult to obtain and valves are frequently assembled with improper spring adjustment.
Furthermore, sliding of the spring biased disk relative to the valve seat causes these parts to wear and produces abrasion powder which enters the fluid flowing through the valve. Gas residues are also produced in the prior art valves because the valve cavity must be large to accommodate the relatively large number of parts and the internal valve structure is complicated. These characteristics make the prior art valves unsuitable for use in certain manufacturing equipment such as that used for making pharmaceutical or semiconductors, or in vacuum apparatus requiring a high degree of purity.